The present invention relates to a roller bearing, and more particularly, a roller bearing having a plurality of rollers circumferentially disposed and each rotatably supported by a retainer.
Generally, a roller bearing includes a plurality of circumferentially located rollers and a retainer with a plurality of supporting holes adapted to support the rollers rotatably. The retainer typically has an outer race and/or an inner race. As a lubricating method of such a roller bearing, applying grease on the retainer, forming a recess as a grease container on the retainer, or oil drip or splash is conducted.
However, in a roller bearing with smaller rollers, especially, in a needle roller bearing, since a thickness of a retainer is thinner and a distance between adjacent supporting holes of the retainer is narrower, it is difficult to form a recess as a grease container between adjacent supporting holes on a retainer. Particularly, in a needle roller bearing with a smaller outer diameter, since a distance between adjacent supporting holes of the retainer is much narrower, it is very difficult to form a recess as a grease container between adjacent supporting holes on a retainer.
Therefore, a prior art roller bearing, especially with smaller rollers and a smaller outer diameter, could not be fully lubricated.
The present invention has been made to eliminate these problems and its object is to provide a roller bearing having an adequate lubricating function even in the case where the bearing is composed of smaller rollers or the bearing has a smaller outer diameter.
A roller bearing of the present invention includes N pieces of rollers disposed circumferentially and parallel to each other, and a retainer adapted to support the rollers rotatably. Each roller has a first and second end portion located axially away from each other. The retainer includes a first, generally cylindrical retainer member having N pieces of first notches adapted to rotatably support the first end portion of each roller and a second, generally cylindrical retainer member that is located axially away from and opposite the first retainer member and that has N pieces of second notches adapted to rotatably support the second end portion of each roller. A plurality of voids are provided to form grease containing spaces between the oppositely disposed first and second notches and the circumferentially adjacent, oppositely disposed first and second notches between the first and second retainer members.
According to the present invention, since the retainer is formed of the first and second retainer members contraposed and located away from each other, and voids for grease are formed between circumferentially adjacent notches of these retainer members, even in the case of a needle roller bearing having rollers of smaller diameters and a retainer of a thinner thickness, or a needle roller bearing with a smaller outer diameter and narrower spaces between the adjacent supporting holes, a grease containing space can be secured and thus, adequate lubricating function can be achieved.
Moreover, in this case, because a grease container is not formed concavely on the surface of the retainer but formed at a void where no other members exist between the first and second retainer members, grease can be directly applied to a rolling contact surface between an inner and outer race member and each roller. Thus, the rolling contact surface can be fully and securely lubricated.
When the first and second retainer members are formed separately, N pieces of voids are provided between the first and second retainer members. In this case, since the same number of grease containers as rollers is formed, each roller can be securely lubricated with adequate amount of grease. Also, in this case, not an elongated aperture but a notch is formed in the first and second retainer member to receive each roller. Thus, in injection molding each retainer member, it can be formed using an axially movable mold. Therefore, a multiple mold can be deployed on the same plane in a molding unit of a forming machine, thereby reducing the cost of a mold and manufacturing cost.
To the contrary, in forming a prior art retainer having a plurality of apertures to hold rollers, an inner mold disposed on an inner circumferential side and a plurality of outer molds disposed on an outer circumferential side and divided in a normal direction are required to compose a mold, and each outer mold needs to be translatable in a normal direction. Thus, the structure of a mold becomes complicated and the only one mold can be disposed at a mold unit of a forming machine to secure a travel space of the outer mold, thereby increasing the cost of a mold and a manufacturing cost.
When the first and second retainer members are connected to each other by n ( less than N) pieces of connections provided at voids and (N-n) pieces of voids are formed between the first and second retainer members, the first and second retainer members can be formed integrally with each other through connections, thus facilitating assembly of a roller bearing. In addition, the first and second retainer members and connections are preferably welded or fused by ultrasonic wave or the like, and alternatively, they may be integrated with each other by plastics molding.
When a cylindrical outer race is further provided and opposite ends of the outer race are supported by the first and second retainer member, the outer race is located on an outer circumferential side of each void formed at adjacent rollers, thereby preventing grease from flying out of the void through centrifugal force. Also, an axial distance between the first and second retainer member can be maintained by the outer race, and the first and second retainer member and the outer race can be integrated with each other, thus facilitating assembly of a roller bearing.
A lip portion of tapered cross section contacting the inner circumference of the outer race may be formed on the first and second retainer member. In this case, by providing such a lip portion, grease which is housed in a void between the first and second retainer members can be prevented from leaking out from the inner circumference of the outer race through a clearance between the opposite ends of the outer race and the first and second retainer members.
An oil groove may be formed at a portion of the first and second retainer member contacting the outer race. Thus, especially in an application where a shaft is fixed and an outer race is rotatable, wear to the retainers due to the difference of the rotational speeds between the retainer and the outer race can be prevented.